Tennis racquets were traditionally constructed with a wood frame, usually ash. In early tennis racquets, the racquet was formed by bending a strip of ash (or a laminate formed of multiple strips of ash) into a hairpin shape, such that the middle portion of the strip formed an open stringing area. The ends of the strip converged in a throat region, and thereafter extended side-by-side to form a shaft. A generally triangular wood block was positioned in the throat region, between the opposite sides of the strip, to form the base of the stringing area.
In later wooden racquets, curved strips of ash extended across the throat area to form, with the remainder of the head portion, a generally oval shaped hoop defining the stringing area. Generally, a splice joint, wrapped by lengths of twine binding, was used to join the wood laminates in the throat area.
More recently, tennis racquets were introduced having hollow tubular metal racquet frames. Such racquets were formed by bending a single length of frame tube to form the head and shaft sections, the latter being formed by the ends of the tube, which converged in the throat and extended side-by-side to form the shaft. A separate throat piece was provided to span the throat area and complete the lower end of a generally oval stringing area. The throat piece was formed of metal or plastic and attached to the sides of the frame in various ways, such as welding, rivetting, or by screws. Such constructions are generally referred to as open throat racquets, in that the throat piece and converging frame sides defined an open area below the throat, located between the two shaft tubes. While metal frame racquets eventually became popular as an alternative to wood, they did not replace wooden racquets, and the two materials co-existed for some years.
In the 1970's, composites, in the form of fiber-reinforced thermosetting resins, were introduced as another frame material for tennis racquets. Initially, composites were not widely used as frame materials, however.
In about 1976, Prince Manufacturing, Inc. introduced the Prince.RTM. Classic, in which the conventional geometry was changed to provide an oversize head, open throat tennis racquet, which greatly improved racquet performance. The Prince racquet, which is the subject of Howard Head U.S. Pat. No. 3,999,756, enjoyed immense popularity.
The Prince Classic racquet was made with an aluminum frame. In the 1980's, composites began to be increasingly used to make racquets utilizing the Howard Head design, i.e., open throat, large head racquets. Today, most tennis racquets utilize the large head geometry of the Howard Head invention (in sizes generally referred to as mid-size, mid-plus, or oversize) in an open throat design and utilize either composites or metal as the frame material.
In the conventional manufacturing process used today, sheets of uncured thermosetting resin, which contain carbon reinforcing fibers, a.k.a. "prepreg", are wrapped around a mandrel, which is then withdrawn to form a hollow tubular layup. A bladder is placed inside the tube and the tube, which at this point is flexible, is placed inside a mold in the shape of a racquet frame. A throat piece is also positioned in the mold, and additional resin material is wrapped around the joint between the throat piece and the frame tube. The mold is then closed and heated to cure the resin. At the same time, the bladder is inflated to force the tube to conform to the shape of the mold.
While almost all metal and composite racquets in the past have utilized the open throat design, composite racquets have been made in which the frame tubes join at the base of the stringing area, and then extend as a single shaft. Examples of such racquets are the PDP and Fischer Superform racquets, which were produced for a time in the 1970's.
The PDP and Fischer Superform racquets were of the pre-Howard Head design, i.e., only about 75 square inches in the head, were very heavy (on the order of 420 grams), and were also very bulky in the throat joint area. Racquets utilizing an open throat construction, in contrast, offered better aerodynamics (due to the fact that two thin frame members are used in the throat), better stability against torsional twisting, and a higher polar moment of inertia than the bulky throat designs of the PDP and Fischer racquets. As a result, the open throat design is almost universally employed in commercial racquets today.
There have also in the past been proposals for making tennis racquets in which the shaft is detachable from the head. However, such a racquet has never been commercially successful.